Rename to stealergram, add pyproject.toml, purge em-dashes

- Rename project to stealergram throughout
- Add pyproject.toml (replaces requirements.txt split, folds pytest.ini)
- Replace all em-dashes with hyphens across all source files

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

requirements.txt

@@ -15,7 +15,7 @@ tqdm
 py7zr
 rarfile
 
-# Web frontend (optional — only needed with --web)
+# Web frontend (optional - only needed with --web)
 fastapi
 uvicorn[standard]
 jinja2